Many MEMS (microelectromechanical systems) devices use “vias” to electrically or mechanically connect one layer to another. The vias are typically made by forming an opening through an intermediate layer, such as by patterned holes or trenches.
An example of a MEMS devices that uses such vias is the Digital Micromirror Device™ (DMD™), manufactured by Texas Instruments Incorporated. The DMD is a fast, reflective digital light switch. It can be combined with image processing, memory, a light source, and optics to form a digital light processing system capable of projecting large, bright, high-contrast color images.
The DMD is fabricated using CMOS-like processes over a CMOS memory. It has an array of individually addressable mirror elements, each having an aluminum mirror that can reflect light in one of two directions depending on the state of an underlying memory cell. With the memory cell in a first state, address electrodes under the mirror are activated to cause the mirror to rotates in one direction. With the memory cell in a second state, the mirror rotates to the opposing direction. Vias are used to conduct electricity from a bias/reset bus under the mirrors to the mirrors themselves or from memory cells to address electrodes.